1. Field of the Invention
The present invention relates to a method for calibrating surfaces of stone materials, ceramics, marble, granite.
2. Description of Related Art
A method for calibrating surfaces of stone materials is classified into the following International Patent Classes (IPC): B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; B28D—WORKING STONE OR STONE-LIKE MATERIALS.
The prior art in calibrating the surfaces of stone materials is given by:
DE4209273, which discloses a method for calibrating surfaces of stone materials and a plant for calibrating slabs of stone material according to the preamble of the relevant Claims. Such a prior document discloses a head with spindles which works on two sides of a slab of stone material not simultaneously, but in a sequence, due to the transverse movement of the cross-member to which it is rigidly connected, thereby providing a head with reduced sizes. Moreover, the head of this prior art document comprises spindles mechanically connected to the central drive shaft, and motored through such shaft.
U.S. Pat. No. 6,783,443: “Polishing machine for stone materials, having multiple grinding heads aligned on two oscillating and parallel beams with variable offset”, in which a machine is disclosed for calibrating stone material comprising a belt conveying the slabs to be calibrated, a pair of beams oscillating along a transverse direction to the conveyor belt motion and respectively supporting a row of calibrating heads, the oscillating beams being arranged at a mutual distance that can be modified.
U.S. Pat. No. 5,056,272: “Method and apparatus for reducing thickness of stone slabs”, in which a machine is disclosed for calibrating the thickness of a slab of stone material through two sets of coaxial discs having the same diameter and respectively arranged along two parallel axes arranged transversally to the advancement direction of the conveyor belt of the slabs of stone material.
U.S. Pat. No. 5,022,193: “Method of automatically gauging articles of granite, hard stones and the like of desired thickness, with discontinuous motion”, in which a method is disclosed for calibrating slabs of stone material advancing through a conveyor belt and subjected to the action of a spindle comprising a diamond tool, the spindle being able to invert the movement direction according to a trajectory in an orthogonal direction to the belt for advancing the slab, the slab advancing discontinuously and being calibrated, when it is not moving, through a transverse movement of the spindle which covers a first section of slab, then, by stopping the calibration and advancing the slab by a distance equal to the width of the first calibrated section, repeating the procedure for the following slab sections.
U.S. Pat. No. 4,914,870: “Process for automatically smoothing and polishing slabs or marble, granite, stones and the like”, in which a method is disclosed for calibrating stone material comprising a system for checking the advancement of the belt for transporting the slab, characterized in that the slab advancement occurs discontinuously and, with an unmoving slab, the beam for supporting the tool-holder spindles performs the transverse motion by calibrating a first slab area for all its width, repeating the procedure for following sections of the slab.
The prior art substantially takes into account:
the continuous calibration by means of a spindle supporting a cylindrical tool whose extension is greater than or equal to the maximum slab width, rotating along a fixed axle parallel to the slab plane and orthogonal to the slab advancement direction. The continuous slab advancement, coupled with the spindle rotation, produces a cutting edge, namely a partitioning line between the calibrated surface and the rough surface that must be calibrated, which covers the whole slab width and advances with the advancement of the slab itself. Approaching the tool with respect to the slab surface occurs by cutting, namely along a direction parallel to the slab surface. For this reason, the continuous calibration works “with position”;
the intermittent calibration through a spindle supporting a tool rotating along an orthogonal axis to the slab plane and translating along a transverse direction to the slab advancement direction. Coupling of transverse translation and rotation around its own axis for the tool-holder spindle, produces a cutting edge which does not cover the slab width, but only a part of it. Approaching the tool with respect to the slab surface occurs through pressure, namely along an orthogonal direction to the slab surface. Due to this, the intermittent calibration works “with pressure”.
The continuous calibration has the advantage of making a cutting edge coinciding with the slab width. It also has the disadvantage of having to have available a supporting structure for the cylindrical tool with high stiffness and therefore with big sizes in order to ensure the uniform slab calibration. Since the slab reaction force, subjected to the distributed action of the cylindrical tool, is maximum at its center, where the cylindrical tool is more inflected, the continuous calibration by means of a transverse cylindrical tool is: efficient along slab edges, namely next to supporting bushes for the cylindrical tool; scarce along the slab center-distance, namely at half the cylindrical tool height.
The intermittent calibration has the advantage of making the tool better suited to the slab profile due to the fact that the cutting edge does not completely cover the beam width. This allows adopting a slim, not necessarily stiff machine structure.
A problem, occurred in these years, deals with the difficulty of obtaining calibrated slabs and complying with always more and more accurate dimensional tolerances.
It is known that the slab, usually coming from sawing by means of blades or from sawing by means of multi-wire frames, has a surface with a high central concavity. In the '90s, it has been deemed advantageous to calibrate the slab by keeping the slab profile concave; this implied making a product with a high degree of surface finish but, at the same time, provided with a strong geometric irregularity.
In spite of the fact that keeping the slab concavity allows reducing waste to be disposed of, due to the lower amount of removed material, nowadays the market requires more accuracy coupled with an extreme brightness quality of the worked material.
The intermittent slab advancement, coupled with the transverse movement of the tool-holder spindle, allows obtaining slabs with high aesthetic qualities, but low geometric accuracy.
Therefore, the calibration with intermittent advancement is not able to satisfy the dimensional requirement required by the marked.